One of the top priorities for Washington environmental groups this year has been promoting a law that would require the addition of ethanol to gasoline. The intention is to reduce dependence on fossil fuels and cut greenhouse gas emissions, while benefiting farmers and building the renewable fuel supply.

But new research suggests the notion might be a little corny — or at least a mixed bag.

That’s because you have to take into account the energy spent and global-warming pollution released creating the fuel from corn or sugarcane in the first place.

A nature.com article on the research, which was published in the journal Science, says this about the University of California, Berkeley study led by Alex Farrell:

“The team found that some studies ignore a few of the side benefits of ethanol production. Farrell and his colleagues argue that products such as corn oil and animal feed, made as by-products of bioethanol production, should be included in the energy budget, because they have economic value and displace competing products that require energy to make.

When these factors are taken into account, biofuel gives more energy back to society than it uses in production, Farrell reports in Science.

But using ethanol rather than petrol in your car only reduces its total carbon dioxide emissions, mile for mile, by about 13%. This is in part thanks to the fact that the agricultural processing needed to create the biofuel itself produces a lot of pollution.”